Known oxy/fuel combustion systems include flue gas recycle equipment, flue gas recycle controls, and/or secondary fuel injection. Known systems have relied upon these features to provide desired temperatures of heat exchange surfaces. These features add to the size and complexity of a system, capital and operating costs of the system, are subject to degradation, and may increase system maintenance needs. Systems incorporating flue gas recycle, in particular, are relatively large due to the relatively large gas volume to be circulated to provide the desired heat profile.
The combustion of coal in a boiler with oxygen, so called oxy/coal combustion, presents two fundamental challenges; one is to maintain the proper balance between radiative and convective heat transfer in heating water to steam, while the other is to protect metal components in the boiler from mechanical damage resulting from the extremely high temperature oxy/fuel flame. In an air/fuel boiler converted to oxy/fuel operation, the most frequent approach is to recycle flue gas with a sufficient volumetric flow rate so that the mixture recycled to the furnace, which essentially comprises O2 and CO2, approximates air (for example, O2/N2). This may require a flue gas recycle mass flow rate of the order of 10-12 times the fuel flow rate.
Therefore, there is an unmet need to provide an oxy/fuel system and method of combustion that do not rely upon flue gas recycle equipment, flue gas recycle controls or secondary fuel injection to provide the desired temperatures of heat exchange surface, wherein the system is of a smaller size, lower cost, and/or more resilient, thus leading to greater efficiency.